(1) Field of the Invention
This invention relates to an implant artificial denture, and more particularly an implant artificial denture which can prevent lesion of the surrounding tissue especially by improving the upper structure thereof.
(2) Description of the Prior Art
Attempts of restoring the function of a decidual or extracted tooth by a so-called implant artificial denture have increasingly been made. For providing an implant artificial denture, an intra-ossal implant or an intra-ossal implant in the tooth (hereinafter referred to as simply intra-ossal implant) is impacted in the jaw to employ it as the dental root, and an upper structure is fitted thereover.
Accordingly, many proposals for artificial dentures, particularly for material, shape, etc. of artificial dentures have been made. Now an improvement in the intra-ossal implant is being made to such an extent that it has such a mechanical strength as to withstand a high masticatory pressure.
However, fixing of the intra-ossal implant in the jaw caused other clinical problems.
In the natural tooth, the chewing and masticatory pressure or shock is absorbed by the absorbing action of the periodontal membrane. Contrary thereto, in an implant artificial denture, the pressure and shock applied to the upper structure are applied directly to the jaw, which induces inflammation of tissue as well as the dissolution and uptake of bone in the neighbourhood of the interface between the intra-ossal implant and the jaw tissue. Therefore, it is usually necessary in an implant artificial denture to make the masticatory surface smaller and smoother so that the pressure or shock applied to the dental root may not be so high, and to reduce the masticatory force by other means, which results in a state at which complete chewing is greatly sacrificed.
Thus the upper structure of conventional implant artificial dentures was at such a state as to be much improved.
Lightening of the load imposed on the artificial denture by fixing it to the adjacent healthy teeth results in injuring the healthy teeth.
In the natural tooth, a shock as in biting a solid foreign body and abnormally high chewing pressure are absorbed by the action of the periodontal membrane, and an excessive pressure or abnormally high shock applied to the tooth or the jaw during chewing or in a state where a biting force is applied thereto is naturally transmitted to cerebral nerves to be controlled accordingly.
However, an implant artificial denture can not provide all the abilities the natural tooth posseses, and has great drawbacks to be solved.
Particularly, the implant artificial denture neither has the periodontal membrane the natural tooth posseses, nor posseses any sensing ability for the transmission of masticatory pressure.
That is, no transmission of masticatory pressure to cerebral nerves is made in the case of the implant artificial denture, so that the pressure and shock applied to the upper structure thereof are applied directly to the jaw, which results in inducing inflammation of tissue as well as the dissolution and uptake of bone in the neighbourhood of the interface between the intra-ossal implant and the jaw tissue, and causing lesion of the implant artificial denture, the surrounding tissue, the jaw joint and the like. These are serious drawbacks of implant artificial dentures.
However, it is generally impossible to join an implant artificial denture to the sense organs of the cerebral nerves. Accordingly, it is necessary to sense the danger due to abnormally high mechanical shock with a stimulation instead of relying upon an exitation of the pain sense which occurs in the case of the natural tooth as described above.
Therefore, the inventors studied the method of sensing the limit of chewing force applied to implant artificial dentures by incorporating a stimulation-producing device in the upper structure of an implant artificial denture, and by sensing the stimulation produced by the device through the internal ear.
It was proved that an abnormally high pressure or shock is sensed and may be voluntarily controlled by the use of an echo device fitted inside a crown of tooth to sense an abnormally high pressure or shock to the patient through the internal ear.